I understand you want to make him LCS-viable, because even though he's a fairly simple champion who isn't particularly flashy, his ultimate chains and even just the potential for them can make things really hyphy (or he falls behind and is the laughing stock of the game).
But the reality is that darius doesn't need direct buffs, not at the expense of lower elos that for whatever reason refuse or otherwise can't learn how to play against darius.
At the very least, make it a very small buff that would be more along the lines of QoL as opposed to number buffing.
Darius's numbers are the strongest they have EVER been in the champion's history, you don't need to continue to powercreep him. A rational approach would be to power-down other champions and/or items that might have powercreeped things a bit.